The Voice US coach Adam Levine has reached out to the family of Christina Grimmie, the 22-year-old singer who was shot dead at her show in Orlando on Friday.

The Maroon 5 frontman has offered to pay for her funeral, her brother Marcus wrote on Facebook.

"I found out this morning, that Adam Levine personally called my mother and said he will pay for the funeral and her plane flight, and I was blown away," Marcus told his sister's fans.

Adam, 37, coached Christina on the sixth season of The Voice in 2014, helping her get to third place.

He wrote on Twitter on Sunday: "Behati [Prinsloo, his wife] and I are absolutely devastated and heartbroken by Christina Grimmie's death. Our hearts go out to her family."

Adam isn't the only celebrity stepping up to help Christina's family after the tragic shooting by Kevin James Loibl, believed to be a "deranged fan".

A GoFundMe page has been launched by Christina's manager, Brian Teefey, the stepfather of pop star Selena Gomez. According to Marcus, the campaign will help the family move out of their home, while also contributing to the funeral.

Nearly 5000 people have donated to the page, raising $237k (US$175k) in just two days.

"Words cannot express…literally I have no words," Marcus wrote in response to the campaign.

"I'm so blown away by everything right now. But all I can say is thank you. And Christina will be missed and never ever forgotten. Love you Christina."

Related video: Christina Grimmie's Voice blind audition

He also asked fans of the late YouTube star not to feel the need to donate anything, but rather sign a Change.org petition to help Christina "be remembered in the next Legend of Zelda game, her favourite game of all time".

Marcus was hailed a "hero" for tackling the shooter, who approached the singer as she was signing autographs outside her concert. The gunman fatally shot himself during the struggle.

Selena Gomez paid tribute to her friend Christina at her latest Miami concert, breaking down during her song 'Nobody' and later dedicating the song 'Transfiguration' to the girl she'd known since her teenage years.

"When she was 14, we met her – my parents and I signed her," Selena said. "And one thing about Christina and her family, is that she holds her faith so closely to her.

"It's not about her religion, and it's not about good deeds. It's just that she had faith. And I don't really understand how this happened, but I would like to dedicate this next song to her."